Border cell situations have existed since the early days of wireless communications. In one border cell scenario, a mobile unit hears a page from one base station and provides a page response to another base station. In another border cell scenario, a mobile unit having registered with one base station moves to another base station without re-registering its new location with the network (or without the network having acknowledged the re-registration) just as a call is being delivered. These scenarios prevent the network from successfully delivering a call to the mobile unit because the network's knowledge of the location of the mobile unit is not up to date. The network expects that the mobile unit is located in the cell where it has last registered but the mobile unit has since moved to a new location (e.g., a border cell) served by a different base station. The net effect of unsuccessful call delivery is a decreased revenue stream for the service operator.
The border cell problem is most exacerbated where the base stations serving the expected location and new location are controlled by different mobile switching centers (MSCs) as would occur, for example, when the mobile unit has roamed between different communication systems. The MSCs serving the expected location and new location are known as the Serving MSC (“SMSC”) and the Border MSC (“BMSC”), respectively. Thus far, efforts to overcome the border cell problem have relied upon dedicated voice circuits between neighboring MSCs/systems. For example, the ANSI-41 Standards for Intersystem Operations prescribe the use of dedicated voice circuits between the SMSC and the BMSC for providing an intermediate call path for an incoming call directed to a mobile unit in a border cell. Such a link using dedicated circuits is known as a “circuit-switched” link. The final call setup appears as a call delivery to the SMSC followed by an intersystem “hard” handoff to the BMSC, where voice coder and speech processing resources for the call are established by the BMSC.
A problem that arises is that dedicated voice circuits between neighboring MSCs/systems are relatively expensive for service providers to purchase, install and/or maintain. It would be desirable for service providers to use packet-based links, which are considered to be more efficient than circuit-switched links, to deliver incoming calls to mobile units in border cells. Examples of packet links include asynchronous transfer mode (ATM), frame relay or internet protocol (IP) links. Such packet-based links are pre-existing (or will soon exist) in many networks, as the wireless industry is migrating from traditional, circuit-based switching technology to packet-based switching technology, although they are not currently prescribed for use in border cell situations.